The Section works on the interaction of (complex) carbohydrate immuno- determinants with monoclonal antibodies (MAbs). The elucidation of this interaction in great molecular detail pertains to all ligand-protein interactions. We are executing: 1. Physico-chemical studies on antibody/antigen systems (Sh. dys. type 1, V. cholera). 2. The synthesis of ligands for affinity studies. 3. The study of immunodeterminants of bacteria causing significant diseases on a global scale (Sh. dysenteriae type 1, V. cholera), so as to evaluate procedures for vaccine development. 4. The amino acid sequencing of immunoglobulins and studies on their tertiary structures. We are continuing to determine the specific interaction between microbial polysaccharides, such as dextran and a number of monoclonal antibodies, Vibrio cholera and its monoclonal antibodies, and have prepared ligands to probe the fundamental nature of these antibody-antigen association. We have prepared additional complex fragments of the capsular polysaccharide of Shigella dysenteriae type 1 by sophisticated syntheses. These include deoxy and deoxyfluoro derivatives of the determinant. Studies are continuing on the binding area of a monoclonal antibodies towards this disease-causing micro-organism. The amino acid sequence of some of these antibodies will be determined by cDNA approaches. Three dimensional structures will be evaluated to delineate actual molecular forces involved in the binding.